1. Field of the Invention
This invention relates to a method for the polymerization of ethylene and, more particularly, to a method for the polymerization or copolymerization of ethylene in the presence of a catalyst substantially composed of a titanium composition which is activated in a specific manner and an organoaluminum compound. All reference hereinafter to polymerization includes also copolymerization.
2. Description of the Prior Art
Several methods for the polymerization of ethylene are known using catalysts of the type which comprises a supported catalyst which is obtained by either supporting a titanium compound on or chemically combining a titanium compound with solid surfaces of various kinds of magnesium compounds, and an organometallic compound in combination therewith. With catalysts of the above-described type, although the polymerization rate of ethylene is increased, the resultant polymer disadvantageously has a low bulk density, so that it is almost impossible to increase concentration of the polymer per unit quantity of polymerization solvent and the rate of polymerization is considerably decreased with the passage of time resulting in extremely poor productivity.
In order to over come this disadvantage, U.S. Pat. No. 3,888,835 describes a method for polymerizing ethylene in the presence of a catalyst containing (a) a composition which is obtained by copulverizing a mixture of titanium tetrachloride or titanium trichloride, a magnesium halide and an aluminum halide-ether complex, and (b) an organoaluminum compound. By this method, polyethylene with high bulk density can be obtained at high yield. Such polyethylene, however, is disadvantageous for certain purposes since it has a rather wide molecular weight distribution. Accordingly, there is a great demand for an improved process for polymerizing ethylene enabling the production of polyethylene having a narrow molecular weight distribution. The present inventors have developed a catalyst useful for the polymerization of ethylene which is far improved over the prior art catalysts.